The present invention relates to the processing of electrical signals in connection with the recording and reproduction of sound, and in particular to the reproduction and the rerecording and playback of previously recorded sound signals.
The applicant is co-patentee of U.S. Pat. Nos. 4,155,041; 4,151,471 and 4,259,742 and is sole patentee of U.S. Pat. No. 4,322,641. These patents, which are incorporated herein by reference, are all concerned with the reduction of extraneous noises in the reproduction of analog sound recordings. These patents disclose three distinctly different and complementary systems for eliminating or reducing noises in the playback of old cylinder and disc records. The first of these systems eliminates noises in the reproduction of monophonic disc or cylinder records by virtue of a switching process that selects reproduction from the momentarily quieter groove wall or from an equal mixture of the two, requiring that the recording be reproduced with two-track, stereophonic equipment. The second of these systems eliminates or greatly reduces the amplitude of noise transients that remain after the switching process. The third system reduces the high frequency “hiss” that is not susceptible to reduction by the first and second systems. The second and third systems are applicable to both monophonic and stereophonic recordings.
The present invention provides new and improved means by which each of these three systems, individually and in combination, provides superior results in the reduction of noises and achieves major reductions in the artifacts which occasionally limited the versatility of the previous devices.
As used herein, the term “input signal” refers to the electrical signal, consisting of generally continuous and transient signals, bearing the audio information intended to be heard by the listener or receiver, plus noise signal. The term “noise signal” refers to the unwanted signals, both continuous and transient, which may be contained in the input signal. The terms “total signal”, “signal plus noise” and “program plus noise” are employed, depending on the context, synonymously with “input signal.” “Program content” or “music signal” refer to the input signal less noise signal.